This invention relates to a novel method for circulating condensation treatment of a regenerating gas in a dry dehumidifier, in particular to a method for removing moisture from gas (air or the like) to be dehumidified containing vapor of a solvent. Particularly, the method comprises the following steps. Namely, at least a part of regenerating outlet gas of the dehumidifier containing a mixture of moisture and vapor of a solvent transited from dehumidified gas is subjected to dehumidification treatment with regard to the moisture contained therein before reusing it as regenerating gas. Preferably, a part of the regenerating outlet side gas is exhausted out and the solvent vapor contained therein is subjected to removal treatment. This makes it possible to increase the vapor concentration of the regenerating gas as well as to miniaturize a gas treating apparatus in case of treating the gas. Further, in case of treating the gas by combustion system, it contributes to the reduction of fuel use.
As a device for reducing moisture contained in gas such as air and feeding dried gas (air) to its using environment, a dry dehumidifier is used and various types of dry dehumidifiers are proposed.
This dry dehumidifier is a device for removing or reducing moisture contained in, e.g., air by bringing this air into contact with dehumidifying materials by utilizing their water-absorbing ability, and the dry dehumidifier is being used widely for dehumidifying gas from low humidity to high humidity.
A dry dehumidifier, as illustrated in FIG. 1, is generally used for dehumidifying moist gas. As regenerating gas used herein, hot air is produced by heating the outside air. This hot air dries a moist dehumidifying rotor. Regenerating outlet gas (air) gets mixed with water discharged by the dehumidifying rotor to be moistened air. This regenerating outlet gas (air) is conventionally discharged as it is into the air.
In case of using a dry dehumidifier for drying equipment and the like and gas to be dehumidified containing vapor of a solvent (gas to be treated) such as air containing the solvent vapor, it is also generally known that moisture as well as the solvent vapor transits from the dehumidifier treating air side to the dehumidifier regenerating gas side (air side). In this case, the dehumidifier plays two roles of removing moisture and removing vapor of a solvent both of which are contained in gas to be treated (air or the like to be treated).
It is proposed for the purpose of improving the performance of the dehumidifier to make a purging zone or to divide a regenerating zone (cf., e.g., JP-A Nos. 6-320/1994, 5-115736/1993, 5-200233/1993, 6-31132/1994, 6-63345/1994, 6-343817/1994 and 6-343818/1994 (The term xe2x80x9cJP-Axe2x80x9d used herein means unexamined laying open of Japanese patent application called xe2x80x9cKokai-Publicationxe2x80x9d).
Commonly in these prior art systems, moistened regenerating outlet air is discharged as it is out into the atmosphere.
In such systems, in case that vapor of a solvent is contained in gas to be treated that should be dehumidified, the solvent vapor transited to the regenerating gas (air) side without removal treatment is discharged into the air together with water.
In recent years, in order to prevent air pollution, it is necessary to remove a solvent contained in the aforementioned dehumidifier regenerating outlet air before discharging it into the atmosphere.
For removing vapor of solvent, a method of introducing the regenerating outlet gas (air) into a device for removing vapor of a solvent is generally applied. With regard to the kind of the devices, there are a lot of systems such as combustion system, absorbing recovery system, cooling recovery system, scrubber system, bio-filtration system and the like.
However, in case of using dehumidifiers of large size, a large-sized device for removing vapor of a solvent (apparatus for treating exhaust gas) is necessary because the quantity of regenerating gas (air or the like) is large, so that huge equipment costs are required.
In case of applying combustion systems (including a Regenerative Thermal Oxidizer) to the exhaust gas treatment apparatus, auxiliary fuel is necessary because the concentration of gas to be treated is dilute, so that there are many cases that running cost becomes high.
There is also a method for condensing the regenerating outlet gas by a dilute gas condensation apparatus (with a zeolite rotor or the like used therein), but this method consumes a lot of energies for removing water because of high humidity, and accordingly running cost becomes high. Further, there is a drawback that many of inferior gases in adsorption efficiency (such as methanol or the like) are discharged into the atmosphere passing through condensers.
Under such circumstances, in case of removing moisture contained in gas to be treated in which vapor of a solvent is contained and which should be dehumidified using a dry dehumidifier, there is much desired in the art to develop an improved method, which enables efficiently the removal treatment of moisture and vapor transited into and thereby contained in the regenerating outlet gas, consequently using small-scale equipments and reducing the treatment costs.
It is an object of the present invention to provide a method enabling the removal treatment of moisture and vapor of a solvent efficiently at low costs with small-scale equipments. Particularly, it is an object of the present invention to provide a method for removing moisture and solvent vapor, from a gas flow containing water and the solvent vapor transited into dehumidifier regenerating outlet gas on the occasion of removing water contained in gas, using a dry dehumidifier.
The present inventors studied assiduously in order to solve the above-described problems, and consequently found that the vapor of a solvent contained in exhaust gas can be condensed efficiently to produce condensed gas of small quantity by circulating and reusing gas regenerated in a dehumidifier such as air used for regenerating gas under specific treating conditions, and thereby made it possible to miniaturize an apparatus for treating vapor of a solvent (exhaust gas) and to reduce totally equipment costs and running cost. The water circulated in the gas regenerating in the dehumidifier and contained in the recycled gas (air or the like) can be removed by cooling dehumidifier or the like. The solvent vapor contained in the exhaust gas can be condensed, sent to an apparatus for treating exhaust gas and treated therein.
According to an aspect of the present invention, there is provided a method for removing moisture from gas containing vapor of a solvent using a dry dehumidifier, said vapor of a solvent in the regenerating gas is simultaneously condensed, comprising the steps of removing moisture from at least a part of regenerating outlet gas of the dehumidifier, and reusing the dehumidified gas as regenerating gas.
It is possible to restrain increase in the concentration of the solvent in the regenerating gas (air or the like) by adding a small quantity of fresh air. According to another aspect of the present invention, exhaust gas (gas containing condensed vapor of a solvent) can be discharged as condensed gas in the corresponding quantity of the fresh air. Consequently, the discharged gas can be treated at low costs using a small-scale apparatus for treating exhaust gas.
In another embodiment of the present invention, the dry dehumidifier has a purge zone and purging outlet gas is used as regenerating gas.
In a further preferred embodiment of the present invention, at least one tenth of the regenerating outlet gas in quantity is circulated and reused.